This specification relates to identifying resources relevant to search queries submitted to a search engine.
Search engines identify digital resources (e.g., Web pages, images, text documents, multimedia content) that are responsive to search queries, and provide information on the identified resources. In general, search engines match terms of the search queries to terms in the resources or metadata associated with the resources to determine which resources are responsive to which queries.
Multiple words can be used to describe a similar concept (for example, “car,” “cars,” “automobile,” and “automobiles”). The word used in or to describe a particular resource may not exactly match the word used in a search query. Therefore, to identify additional resources relevant to search queries, some conventional search engines perform query expansion, augmenting search queries with synonyms for words in the queries. For example, a search query for “red car” could be augmented to be “red (car OR cars OR automobile OR automobiles),” because “car,” “cars,” “automobile,” and “automobiles” have similar meanings. However, because search queries often include multiple terms, and each term in a search query can have multiple synonyms, it can be difficult to add all relevant synonyms to a received search query.